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.Dd March 18, 2021
.Dt CHROOT 8
.Os
.Sh NAME
.Nm chroot
.Nd change root directory for a command
.Sh SYNOPSIS
.Nm
.Ar newroot
.Ar command
.Sh DESCRIPTION
The
.Nm
utility causes
.Ar command
to be executed relative to
.Ar newroot .
The meaning of any initial slash
.Pq /
in the path names is changed to
.Ar newroot
for
.Ar command
and any of its child processes.
Upon execution, the initial working directory is
.Ar newroot .
.Pp
Notice that redirecting the output of
.Ar command
to a file, such as in:
.Pp
.D1 Nm chroot Ar newroot Ar command Sy > Pa xyz
.Pp
will create the file
.Pa xyz
relative to the original root of
.Ar command ,
not the new one.
.Pp
The new root path name is always relative to the current root.
Even if a
.Nm
is currently in effect, the
.Ar newroot
argument is relative to the current root of the running process.
.Pp
This command can be run only by the super-user.
.Sh EXIT STATUS
The exit status of
.Nm
is the exit status of
.Ar command .
.Sh OPERANDS
The following operands are supported:
.Bl -tag -width Ar
.It Ar newroot
The new root directory.
.It Ar command
The command to be executed relative to
.Ar newroot .
.El
.Sh EXAMPLES
.Sy Example 1
Using the
.Nm
Utility
.Pp
The
.Nm
utility provides an easy way to extract
.Sy tar
files
.Pq see Xr tar 1
written with absolute filenames to a different location.
It is necessary to copy the shared libraries used by
.Sy tar
.Pq see Xr ldd 1
to the
.Ar newroot
filesystem.
.Bd -literal -offset indent
example# mkdir -p /tmp/lib /tmp/usr/lib
example# cd /lib && cp ld.so.1 \e
         libavl.so.1 libc.so.1 libcmdutils.so.1 libcustr.so.1 \e
         libm.so.2 libmd.so.1 libmp.so.2 libnsl.so.1 \e
         libnvpair.so.1 libsec.so.1 libsecdb.so.1 libtsol.so.2 \e
         libuutil.so.1 /tmp/lib/
example# cp /usr/lib/libidmap.so.1 /tmp/usr/lib/
example# cp /usr/bin/tar /tmp
example# dd if=/dev/rmt/0 | chroot /tmp tar xvf -
.Ed
.Sh SEE ALSO
.Xr cd 1 ,
.Xr ldd 1 ,
.Xr tar 1 ,
.Xr chroot 2 ,
.Xr ttyname 3C ,
.Xr attributes 7
.Sh NOTES
Exercise extreme caution when referencing device files in the new root file
system.
.Pp
References by routines such as
.Xr ttyname 3C
to
.Dv stdin ,
.Dv stdout ,
and
.Dv stderr
will find that the device associated with the file descriptor is unknown after
.Nm
is run.
